As a former dealer, I hav seen the rotating tang used to attach the mainsheet to it allowing for the attachment tang to rotate while other mainsheets were attached to a fixed bail. I note a topping lift attached temporarily to the tang.
If it is furling boom, generally the other end is spring loaded in a fixed position and by pulling the boom out, the boom could rotate. Not sure in this case but would suggest a different tie off for the topping lift leaving the mainsheet to rotate.
As for the bolt it has loosened inside and you have to drill out the pop rivets removing the end to tighten up. Suggest two nuts with use of locktite tightened together.
As for the topping lift I suggest a curved base cheek block attached to the end of the boom routing down one side of the boom to a cleat